Generally, the space between the lower surface of a trailer between the rear wheels and the forward trailer support is wasted in that it is not utilized to carry cargo. It has been suggested that this space can be used to carry pallets on a return trip. It has also been suggested to provide a frame which receives a container for transporting perishable goods.
Trailers have been built wherein the floor of the trailer is lowered between the rear wheels and the front support to use the wasted space. However, such trailers are inconvenient to load because of the sloping floor.
If the space between the rear wheels and the support is used for carrying cargo, there is a substantial increase in revenue because of the additional cargo which can be transported. Desirable would be a standardized container which can be independently loaded, unloaded, moved, stored, and which can be easily secured to the underside of a trailer between the rear wheels and the front support.